Planar electron tubes



Nov. 26, 1957 T. L. EVANS PLANAR ELEcTRoN 'rBEs Filed April 19, 1954vv INVENTOR THOMAS |EvANs y PLANARELECTRON TUBES Thomas L. Evans, Hicksville, N. Y., assignor to Sylvania Electric Products liuc., a corporation of Massachusetts Application April 19, 1954, Serial No. 424,239

7 Claims. (Cl. 313-270) The invention relates to planar type electron tubes wherein the electrode elements are in the form of laminations, and in particular to -tubes wherein the dimensions are exceedingly small and in which the dimensions are held to very close tolerances. For example, in one type of tube the spacing between grid and cathode is of the order of .003 inch and the tolerance is .of the order of .0008 inch around bogey. In .the past it has been found diicult to maintain the necessary tolerances due to the wide variation in size of the unassembled insulating elements of the tube, for -example the size .of ceramic supports or spacers, and to grind or otherwise bring these insulators down to size is difficult to -either by reason of the fragile character of the ceramic or its hardness or both. For the sake of ruggedness and resistance characteristics it has been found desirable to luse such ceramics as alumina, steatite and Zircon. But in tiring these articles to form, it has not been possible to maintain size standards with suiicient preciseness.

I have found that by constructing a planar Vtube of ceramic material with metal elements as the means for determining the critical spacing of the electrode elements, the variations in size of the ceramics can be overcome easily. Also it is found that it is much easier to fabricate a tube of the kind referred to above utilizing the metal spacers.

It is therefore an object of my invention to construct a planar tube with metallic elements to provide a reference surface from which other elements are to be spaced.

It is a further object of the invention to simplify a planar tube by reducing the number of elements entering into its construction.

A still further object of my invention is to provide a novel support for a cathode.

It is yet another object of the invention to provide a structure which will enable easy assembly of parts.

These and other objects will appear after reading the following specification in conjunction with the accompanying drawing in which:

Fig. l is a cross sectional View through the tube.

Fig. 2 is an exploded view of the tube and Fig. 3 is a view showing the preferred parts ready to be assembled into tube form.

Referring to the drawings in greater detail, there is illustrated a stem base preferably of ceramic material such as alumina, steatite or Zircon. The base is a fairly thick disc, circular in plan, and provided with an annular shoulder 12 on which rests a metallic thimble 14, of low heat conductivity and low co-eicient of expansion approaching that of the ceramic material selected as the envelope of the tube. A metal found satisfactory with alumina is No. 4 alloy, which is an alloy consisting of 6% chromium, 36% nickel and 58% iron. The thimble includes a flange 16 for seating on the shoulder 12 and said flange is wider than the shoulder to facilitate connection of the cathode with an outside circuit. Upstanding from the flange and integral therewith is a circular hollow post 18 having two arcuate projections 20 ICC with inturned ends 22, and integral with these inturned ends is a box frame 24 of any desired conliguration but here shown as rectangular in plan and with vertical walls, the narrow sides 26 of lthe rectangle being joined with the inturned ends 22 and the longer thin sides 28 of the rectangle spanning the space between the projections 20 to afford a means to which a cathode sleeve may be secured. The thimble is braZed in air tight relationship with lthe base 10 as indicated at 3i). Surrounding the thimble and brazed to the flange-i6, inward of the outer periphery of the flange, as indicated at 32, is the frustoconical cylinder 34, which may also be of alumina, Zircon or the like.

Secured to the upper face of the frustum, as by brazing, as indicated at 36, is a metallic annulus 38 which is preferably of stainless steel. The parts are so made that regardless of slight irregularities in the manufacture of the frustum 34, the top face Aof the annulus and the top face of the rectangular box are coplanar. To insure that this coplanar relationship exists, after the parts already described have been assembled, the faces of the box and of the ring are ground down simultaneously by a single planar element covering .both faces to insure that they shall be coplanar.

Mounted on the upper face .of ,the bor frame is the cathode sleeve 4G. The cathode sleeve is preferably spot welded to .the .long side fof .the rectangle -as at 42, there being single spot welds to the walls of the frame near leach end of the `cathode sleeve. The cathode sleeve is preferably .a .nickel sleeve, rectangular in cross section with a tapered end .as shown at 44, the ytapered end forming an overhanging end over the cathode heater leads to electrostatically shield the leads from the grid and anode.

The heater to be inserted into the cathode sleeve is shown at 46 in Fig. 3, the same being an insulated lament with tabs 48 to be welded to the heater stem leads Sil projecting through and suitably sealed within the base l0. Also projecting through the base and sealed thereto is the getter support rod 52 supporting a getter arm 54 for supporting the getter material 56. Since the cathode is spot welded only to those thin walls 28 of the rectangular box which span the space between the arcuate sections 20, and which walls easily may be warped sideways under expansion of the cathode, the cathode is relatively free to expand longitudinally, and, in practice, extremely small displacement of the cathode sleeve in a direction toward the grid takes place, thus avoiding shorting of elements or changes in operating characteristics due to slightly variable heating conditions which may take place in actual use of the tube, either due to variable ambient temperatures or changes in voltages applied to the tube.

As a means to space the grid from the upper face of the cathode there is employed a metallic ring 5S, as of nickel, it being possible to hold the thickness of this metal ring to very close tolerances. This ring is brazed to the ring 38.

Brazed to the ring 58 is an assembly consisting of the grid 60 and the anode 62 supported by a ceramic cap 64 of alumina or the like. The grid is constructed of grid laterals of tungsten brazed on an annular frame of molybdenum or a moly-manganese alloy. The grid laterals 66 face the cathode. The anode 62 is of a metal, preferably molybdenum, and is integral with the lower end of a molybdenum stud 68, the stud passing through an aperture 70 in the cap. The stud is brazed in place by fusing a ring 72 of molybdenum or molybdenum alloy about the stud.

Having described the invention what is claimed as new is:

l. A cathode and cathode support comprising a pillar terminating at its upper end in two opposite spaced apart legs, a hollow frame with thin upstanding walls supported by said legs with two opposite walls spanning the space between the legs, and a cathode having a cathode sleeve rectangular in cross section lying athwart the upper edges of the spanning walls and secured thereto, the give of said spanning walls allowing for thermal expansion and contraction of said cathode sleeve.

2. A sub assembly for an electronic tube comprising a base portion, a bottom tubular ceramic envelope portion supported at one end by said base portion, a metallic washer secured to the other end of the tubular portion, and a cathode support mounted on the sub assembly and having an upper planar supporting surface coplanar with the top surface of the washer.

3. A sub assembly for an electronic tube comprising a base portion, a bottom tubular ceramic envelope portion supported at one end by said base portion, a metallic washer secured to the other end of the tubular portion, a cathode support mounted on the sub assembly and having an upper planar supporting surface coplanar with the top surface of the washer, and a flat cathode secured to said planar supporting surface.

4. A sub assembly for an electronic tube comprising a base portion, a tubular bottom ceramic envelope portion supported at one end by said base portion, a metallic washer secured to the other end of the tubular portion and a cathode support mounted on the sub assembly and having an upper planar supporting surface coplanar with the top surface of the washer, the upper end of the support being in the form of a hollow rectangular box frame with its boundary in the form of upstanding walls.

5. A sub assembly for an electronic tube comprising a base portion, a tubular bottom ceramic envelope portion supported at one end by said base portion, a metallic washer secured to the other end of the tubular portion and a cathode support mounted on the sub-assembly and having an upper planar supporting surface coplanar with the top surface of the washer, the upper end of the sup- A port being in the form of a hollow rectangular box frame with its boundary in the form of upstanding walls, and a at cathode, rectangular in cross section, with one of its sides secured to two opposite walls of the box frame at the upper edges of said walls.

6. An electronic tube having a bottom section including a base portion, a bottom tubular ceramic envelope portion supported at one end by said base portion, a metallic washer secured to the other end of the tubular portion, a cathode support mounted in the bottom section and having an upper planar supporting surface coplanar with the top surface of the washer, and a ilat cathode supported by said surface, said tube also having an insulating cap section including a flat anode mounted in the cap section, and parallel to said planar surface a at grid supported by said cap section beneath and in spaced relation to the anode, said grid also being parallel to said planar surface, and means spacing the grid from said planar surface in close proximity to but above the cathode, and said tube including means sealing the bottom section and cap section together to effect an air-tight seal for the electrodes within the tube.

7. In a planar tube, a support member of thin sheet metal, said support member having opposite walls, long thin narrow sides spanning said walls and a cathode sleeve athwart said sides, lying on the edges of said sides and securely fastened to said edges.

References Cited in the le of this patent UNITED STATES PATENTS 2,133,492 Vatter Oct. 18, 1938 2,365,518 Berkey et al Dec. 19, 1944 2,381,632 Watrous Aug. 7, 1945 2,459,277 Halstead et al Ian. 18, 1949 2,462,921 Taylor Mar. 1, 1949 2,481,026 Law et al. Sept. 6, 1949 2,615,145 Rydebeck Oct. 2l, 1952 

